Malaria causes more mortality globally than any other parasitic disease, yet a full understanding of protective immune responses and disease pathophysiology is lacking, and effective treatments for severe malaria are limited. Nitric oxide (NO) has antimicrobial effects in vitro against a wide variety of organisms including Plasmodium falciparum. In addition, NO has anti-disease effects against malaria in vivo. Our detailed field studies (in both African children and Indonesian adults) have shown a highly significant inverse association between disease severity and blood mononuclear cell (PBMC) inducible NO synthase (NOS2) expression and systemic NO production. We have discovered novel polymorphisms in NOS2 and related genes that are significantly associated with NO production and resistance to severe malaria. This proposal is designed to continue our NIH-funded work to clarify the role of NO in clinical immunity to malaria and protection from severe malaria. We will extend our current case-control studies in Tanzania and Irian Jaya to confirm the association of our newly identified polymorphisms with disease manifestations and severity, and we will undertake functional studies of these polymorphisms in healthy subjects and those with malaria. In longitudinal studies of patients with both severe and uncomplicated malaria, we will investigate the relationship between the ability of host PBMC to express NOS2 and the susceptibility to severe malaria. Our aims are (1) to characterize the association of novel NOS2 and related genetic polymorphisms with malaria disease severity in two separate populations; (2) to determine the functional significance of these malaria-related NOS2 polymorphisms (both in vitro and in vivo); and (3) in longitudinal studies, to determine whether PBMC NOS2 expression and activity relate directly to an individual's susceptibility to severe malaria. Accomplishing our stated goals will be very significant in adding to the understanding of host resistance to malaria infection and resistance to severe malaria. Also, information learned from this work will likely be applicable to other infectious diseases.